Hydraulic apparatus



Ma 10, 970 J. A. NICHQLLS 3,499,285

HYDRAULIC APPARATUS Filed July 18, 1968 4 Sheets-Sheet 1 INVENTOR BY James /Ao/AY @VM' WM P ATTORNEY March 10, 1970 Filed July 18, 1968 J. A. NICHOLLS HYDRAULIC APPARATUS 4 Sheets-Sheet 2 INVENTOR Twas H. NZeAO/I BY MW, CMZM v Wave ATTORNEY March 10, 1970 A, NICHOLLS 3,499,285

, HYDRAULIC APPARATUS Filed July 18, 1968 4 Sheets-Sheet 5 INVENTOR JZJMGSH. X/aAo/l:

BY 3AM S'MEp-m l/halffiaum ATTORNEY March 10, 1970 J. A. NICHOLLS 3,499,235

HYDRAULIC APPARATUS Filed July 18, 1968 4 Sheets-Sheet 4 INVENTOR WM a wmewq, ATTORNEY United States Patent US. CI. 60-53 16 Claims ABSTRACT OF THE DISCLOSURE This invention provides a compact hydrostatic power transmission and comprises a swash plate pump in hydraulic connection with a tilting head motor. Preferably the tilting head motor is of the kind in which the tilting head is carried by arcuate lands for movement about an axis transverse to the motor drive shaft aXis for variation of motor displacement. The swash plate pump may be of the kind in which either the cylinder block rotates and the swash plate is non-rotary or the swash plate rotates and the cylinder block is non-rotary. Preferably the pump cylinder block is mounted in side by side relation with the motor cylinder block and the valve means for the pump and motor are at similar ends of their cylinder blocks so that the hydraulic connections are quite short.

This invention relates to hydrostatic power transmissions.

In accordance with the present invention a hydrostatic power transmission comprises a swash plate pump in hydraulic connection with a tilting head motor.

A swash plate pump may comprise a rotary cylinder block directly connected for rotation by a drive shaft, cylinders in the block parallel to or inclined to the block rotation axis, pistons in the cylinders, a swash plate engageable by the pistons during block rotation to reciprocate the pistons in the cylinders, and valve means located at the end of the block remote from the swash plate to connect the cylinders alternately to supply and return ports in synchronism with cylinder block rotation.

Alternatively a swash plate pump may comprise a rotary drive shaft having a swash plate secured to the shaft for rotation therewith, a fixed cylinder block having cylinders parallel to or inclined to the shaft rotation axis, pistons in the cylinders engaging the swash plate for reciprocation by the swash plate during shaft rotation, and valve means located at the end of the cylinder block remote from the swash plate to connect the cylinders alternately to supply and return passages in synchronism with rotation of the shaft.

A tilting head motor comprises a drive shaft mounted in bearings for rotation but restrained against transverse movement, a titling head tiltable about an axis transverse to the drive shaft axis, the head containing a rotary cylinder block having pistons reciprocated by rotation of the shaft with a stroke dependent on the tilt angle between the head and the shaft, and valve means carried at the end of the cylinder block remote from the drive shaft. The tilting head may be supported by arcuate lands for its tilting movement. Alternatively the tilting head may be supported in a yoke carried by trunnions for its pivot movement.

Where the motor includes arcuate lands the pump cylinder block and the motor cylinder block are preferably arranged in side by side relation and the valve means of the pump and the motor cylinder blocks are arranged at similar ends thereof whereby short passages may interconnect the pump and the motor valve means.

The motor cylinder block may be driven by its drive shaft through the medium of a constant velocity universal joint.

Alternatively limited articulation means may be provided between each motor piston and its associating connecting rod to effect a rotary drive from the drive shaft onto the cylinder block.

The pump is preferably arranged so that it can operate at maximum pump displacement and maximum transmission pressure, these conditions representing the maximum driving torque which the pump will' absorb from the power source driving the pump. When the power source is arranged to rotate at a constant speed this maximum driving torque will correspond to a maximum driving power. At maximum driving torque into the pump the speed ratio of the transmission, i.e. the ratio of motor,

speed to pump speed is adjusted by variation of motor displacement.

The swash plate pump is preferably arranged so that the drive shaft extends completely through the cylinder block whereby one end of the shaft may be connected to drive an auxiliary load.

Preferably the transmission is arranged within a casing which forms a reservoir for the working liquid, the pump and motor drive shaft being arranged in parallel relation and the motor tilting head being arranged to move close to the pump cylinder block when the motor is reduced to a very small displacement.

How the invention can be carried into effect will now be particularly described with reference to the accompanying drawings in which,

FIGURE 1 is a longitudinal cross-section through one embodiment of the invention,

FIGURES 2 and 3 are cross-sections through part of the FIGURE 1 embodiment taken in planes parallel to the plane of FIGURE 1,

FIGURE 4 is an elevation of one component used in FIGURE 1,

FIGURE 5 is an elevation of another component used in FIGURE 1, and

FIGURES 6 and 7 are longitudinal cross-sections taken through a second embodiment of the invention.

Reference is made initially to FIGURES 1 to 5 of the drawings. The transmission shown in this embodiment is intended for use on an agricultural tractor for the transmission of power from the engine to the ground engaging wheels. The transmission is housed in a casing 1 constructed as a structural member of the tractor to be fitted between the engine and the rear axle casing. The opening 2 of the casing is intended to fit onto the end of the engine and for illustration purposes the fly Wheel 3 of the engine is shown in position in the opening 2. A drive shaft 4 extends from the centre of the fly wheel into an internally splined shaft 5 supported in bearings 6 and 7 within the casing 1. The shaft 4 is suitably splined to transmit driving torque to the shaft 5. A pair of gear wheels 8 and 9 are fixedly mounted on the shaft 5 and these gear wheels respectively mesh with the pair of gear wheels 11 and 12. The gear 11 is carried by a hollow shaft 13 supported by bearings 14 and 15 for rotation. The gear 12 is carried within the casing by bearings 16 and 17 and is secured to a shaft 18 extending co-axially through the shaft 13. The shaft 18 extends from the left hand end of the casing 1 to form a power take-off shaft 19. The gears 8 and 11 are proportioned so that haft 13 rotates at a slightly higher speed than shaft 4 whilst the gears 9 and 12 are proportioned so that shaft 18 rotates at a slower speed than the shaft 4.

The shaft 13 is the pump drive shaft. A rotary cylinder block 21 is secured to the shaft 13 by means of driving splines 22. The cylinder barrel 21 contains a number of cylinders 23 all parallel to the axis of rotation, each having a cylinder port 24 opening into a flat surface 25 of he block situated at the right hand end thereof as seen in the drawing. A piston 26 is slidably mounted in each :ylinder 23 and a ball joint 27 at the outer end of each piston secures the piston to a slipper 28. All slippers 28 engage the flat surface 29 of a swash plate 31 which is supported in semi-cylindrical trunnions 32 secured to the :asing 1. The angular position of the swash plate 31 is determined by a servo piston 33 slidably mounted within 1 servo cylinder 34. A connecting rod 35 extends in a sealed manner through one end of the cylinder 34 for :onnection by means of a pivoted link 36 to the swash plate. The servo motor, formed by the piston 33 and cylinder 34, is of a differential area kind in that the working volume defined between the piston, the piston rod and the cylinder is constantly fed with liquid at high pressure and the working volume 37 defined between the piston and the cylinder at the end opposite to the rod 35 is fed with an adjustable pressure in a manner to be described.

The slippers 28 are held in contact with the swash plate surface 29 by means of a retaining plate 38 secured to the swash plate 31 but rotatable relatively thereto.

A valve plate 39 is fixedly supported to contact the surface 25 of the cylinder block, the valve plate including a pair of conventional kidney shaped ports (not shown).

The valve plate 39 is fixedly mounted on a connecting block 41 which is shown in more detail in FIGURE 4. The valve plate 39 is fixedly secured by dowel pins 42 so that the arcuate ports within the valve plate make sealed hydraulic connections with a pair of passages 44 and 45 which extend within the block 41. The passages 44 and 45 open at ports 46 and 47 into a pair of co-axial arcuate lands 48 and 49 adjacent to the surface 43. The passages 44 and 45 form the hydraulic connections between the pump and the motor and for convenience the connecting block 41 also includes a conventional valve assembly 51 which includes such valves as priming valves, an unloading valve, a high pressure relief valve, and a priming pressure relief valve.

The tilting head hydraulic motor basically comprises a motor drive shaft 52, a drive flange 54 integrally formed with the drive shaft 52 and a tilting head assembly 55 slidably mounted on the arcuate lands 48 and 49. The drive shaft 52 is suitably carried by radial thrust bearings 56 and an axial thrust bearing 57. The drive flange 54 includes a plurality of recesses 58 each containing a socket member 59 engaging a ball 61. Each of the balls 61 is integrally formed at the end of a connecting rod 62 which at its opposite end is formed with another ball joint 63 engaged within a piston 64. The piston 64 is slidably mounted within a cylinder 65 formed within a rotary cylinder block 66. Each cylinder 65 connects to a port 67 which opens into a flat surface 68 at the end of the block 66 remote from the drive flange 54. The ports 67 cooperate With a pair of arcuate ports 75 and 76 (FIGURE formed within a valve plate 69 on which the block is arranged to rotate. The block is correctly located on the valve plate 69 by means of a central spindle 71 secured to the valve plate and engaging centrally within the block 66. A spring 72 ensures that initial sealing force is exerted between the block 66 and the valve plate 69. The surface of the valve plate 69 remote from the drive flange 54 includes a pair of projecting lands 73 and 74 of arcuate shape which engage the arcuate lands 48 and 49. As seen in FIGURE 5 the two lands 73 and 74 enclose ports 77 and 78 which are in connection with the arcuate ports 75 and 76 of the valve plate 69. The dimensions of the ports 77 and 78, the lands 73 and 74, the arcuate lands 48 and 49 and the ports 46 and 47 are such that over the full range of angular tilting movement of the head 55 sealed hydraulic connections are effected on the one hand between ports 78 and 46 and on the other hand between ports 77 and 47.

The axle 74 is securely fixed by a key 171 into the valve plate 69 and a head 172 of the axle 71 projects beyond the arcuate lands 73 and 74 into a slot 173 formed in the connecting block between the arcuate lands 48 and 49. The head 172 includes a pair of opposed flat surfaces 174 which accurately fit between the walls of the groove 173 and serve the purpose of accurately locating the valve plate 69 on the arcuate lands 48 and 49 and of preventing the valve plate from twisting on the arcuate lands 48 and 49. The spring 72 acts between the axle 71 and the cylinder block, a rotary bearing 175 acting to accommodate relative rotation between the block 66 and the axle 71. The spring 72 acts only to hold the cylinder block 66 on the valve plate 69 to provide initial engagement. However in order to provide initial engagement of the valve plate 69 on the arcuate lands 48 and 49 one or more springs 176 may be provided in the cylinder or cylinders 87 to effectively react from the trunnion to urge the valve plate onto the arcuate lands 48 and 49.

In order to rotate the cylinder block 66 at the same speed as the motor shaft 52 a constant velocity universal joint 79 is provided in a recess 81 in the drive flange 54 and a shaft 82 extends from joint 79 to a spline connection 83 within the block 66.

For the purpose of adjusting the tilt angle of the head 66 a bell crank lever 84 is mounted on a trunnion 85 secured within the casing co-axially with the centre curvature of the arcuate surfaces 48 and 49. One end 86 of bell crank 84 engages in a convenient cylindrical bore 87 within valve plate 69. The other end 88 of the bell crank lever is provided with a pivotal connection 89 secured to the piston rod 91 of a servo piston 92. The servo piston is slidably mounted in a cylinder 93 secured to the casing 1. Again the servo motor is of a differential area type and the working space enclosed by cylinder 93, piston 92 and connecting rod 91 is permanently connected to a high pressure zone. The opposite end of the cylinder 93 to the connecting rod 91 provides a working space 94 which is connected to a pressure source of control of the servo motor in the manner to be described. Two bell crank levers 84 may be provided, one on either side of the block 55.

For control of the swash angle of swash plate 31 and the tilt angle of the head 55 a pair of control rods 95 and 96 are provided which extend from the casing 1 to any suitable control means operable by the tractor driver. The control rod 95 for the pump is connected as shown in FIGURE 3 to a floating lever 97 by a pivot 98. The opposite end of lever 97 is connected by pivot 99 to a lever 101 secured to the swash plate 31. The centre point of lever 97 is pivotally connected to valve 102 at a pivot 103. The function of valve 102 is to supply liquid either at low or high pressure to a pasage 104 dependent upon the actual position of valve 102 which in turn will depend on the relative positions of the pivots 98 and 99. The passage 104 is connected to the working space 37. The two pivots 98 and 99 both make provision for a small degree of sliding movement as well as pivotal movement.

FIGURE 2 illustrates the servo motor control for the motor. In this case the rod 96 is pivotally connected at pivot 105 to the floating lever 106. The opposite end of lever 106 is connected by pivot 107 to a link 108 which in turn is pivotally connected by pivot 109 to the bell crank lever 84. Both pivots 105 and 107 provide for a small degree of sliding movement as well as pivotal movement. The central part of lever 106 is connected by pivot 111 to a control valve 112 whose function is to supply liquid at high or low pressure to a passage (not shown) connected to the working space 94.

Within the casing 1 the shaft 18 drives two pumps 113 and 114 both of the internal gear type. The delivery of pump 113 is arranged to supply liquid at pressure for the two servo motors whilst the pump 114 is arranged to deliver liquid at low pressure through the valve system 51 into the transmission to maintain it primed with liquid. The whole casing 1 may be adequately sealed where the various shafts pass through so that the casing may form a reservoir for the working liquid of the transmission.

In operation the engine will rotate the drive shaft 4 at a governed speed of about 2000 rpm. The gears 9 and 12 will then supply power at reduced speed of about 1500 rpm. to power take-ofl shaft 19. The gears 8 and 11 will supply power at a slightly increased speed of about 2500 rpm. to the shaft 13 which in turn will rotate the cylinder barrel 21. The pistons 26 will reciprocate in accordance with the angular setting of the swash plate 31 and liquid at pressure will be delivered to one or the other of the passages 48 and 49. The liquid at pressure will then pass into one or the other of the arcuate ports 75 and 76 of the motor valve plate and liquid pressure is supplied to cylinders 65 so that the pistons 64 under pressure will apply a driving torque to the drive flange 54 which in turn wil rotate the drive shaft 52. The drive flange 54 will drive the'universal joint 79 to rotate the cylinder block 66 in exact synchronism with drive shaft '54. The driver of the tractor may be provided with individual controls for the rods 95 and 96 or alternatively a cam device may be provided to effect sequential operation. For starting the vehicle from rest the rod 95 initially is moved to cause servo piston 33 to give maximum displacement in one direction to the swash plate 31 whilst the motor head 55 is maintained at its maximum tilt angIeQ The pump is designed so that at maximum swash angle it is capable of developing the maximum transission working pressure. Therefore it follows that the selection of an angle other than neutral for the swash plate 31 can supply liquid at maximum pressure to the motor head 55 at maximum tilt angle thereby ensuring the capability of maximum driving torque to the motor shaft 52. After the pump swash angle has been raised to a maximum, further increase in tractor speed is accomplished by reducing the tilt angle of the head 55 by appropriate operation of the control rod 96. In both of the valves 102 and 112. the operation is such that the appropriate servo motor will move until the angle of the swash plate or tilting head maintains a position which corresponds to the selected position for the rod 95 or 96 at which point the valve will close off the working space of the servo and hold the swash plate or motor head in that position.

In operation of the motor the axial load exerted by the pistons on the drive flange '54 is reacted on the casing through the thrust bearing 57. The liquid at pressure in the motor cylinders will also react through the motor valve plate 69 and the arcuate surfaces 48 and 49 to exert a very substantial force on the connecting block 41. This is resisted by providing very secure fixing between the connecting block and the casing 1.

The design of the motor by virtue of the shape of the arcuate lands 48 and 49 and the use of the universal joint 79 enables the tilt angle of the head 55 to extend a maximum of 35.

Reference is now made to the embodiment shown in FIGURES 6 and 7 of the drawings. There is a substantial degree of similarity between the two embodiments and similar reference numerals are used to indicate similar parts. Description will only be given of the important points on which the second embodiment differs from the first embodiment. The principal difference lies in the construction of the tilting head motor. The drive flange 54 is provided with a plurality of recesses 114 each of which extend completely therethroughp Each recess accommodates a slipper 115 which is connected to connecting rod 62 by means of the ball joint 61. The slipper 115 bears directly on a wear plate 116 which is supported on the housing of bearing 56. Each of the pistons 64 is of very substantial length so as almost completely to enclose the connecting rod 62. By this means the articulating movement of each connecting rod 62 within its piston 64 is limited to a small amount. Rotation of the drive flange 54 will apply rotational drive to the slippers 115 which in turn move the connecting rods 62 to cause them to engage against the sides of their pistons 64 to apply rotary drive to the cylinder block 66. A spigot 117 extending from the centre of the cylinder block 66 terminates in a ball joint 118 which locates in a socket 119 in the centre of the drive flange 54 to provide accurate location for the cylinder block on its valve plate.

The spring 72 in cylinder block 66 is differently arranged from the FIGURE 1 embodiment in that the spring reacts between the ball joint 118 and the cylinder block thus providing an initial engaging force acting through the cylinder block onto the valve plate 69 and from the valve plate 69 onto the arcuate lands 48 and 49.

For the purpose of retaining the valve plate 69 accurately seated on the arcuate lands 48 and 49 a pair of flanges 178 are provided one on either side of the connecting block in the neighbourhood of the valve plate 69 to engage the ends of the valve plate thus to prevent it from in any way twisting on the arcuate lands 48 and 49.

Operation of the FIGURE 6 embodiment is exactly as described for the FIGURE 1 embodiment the only exception being the exact method of operation of the motor which has already been referred to. The driving of the motor cylinder block 66 through the connecting rod 62 places a limit on the angular movement of the tilting head 55 and in the FIGURE 6 embodiment the maximum tilt angle of the motor head is 25 whereas in 3the FIGURE 1 embodiment the maximum tilt angle is 5.

The advantage gained by the present invention lies principally in the compact size of the hydrostatic transmission which results. FIGURE 7 illustrates the comparatively narrow width of the whole transmission of both FIGURES 1 and 6. The narrow width as shown in FIG- URE 7 results principally from the use of a tilting head motor having arcuate surfaces 48 and 49 to supply liquid at pressure. The side by side arrangement of the pump and motor cylinder blocks also adds to compactness and the very short hydraulic connecting passages 44 and 45. The use of a swash plate pump facilitates the provision of a power take-ofi shaft which extends completely through the pump providing a power take-off connection 1n a very simple manner.

The pump illustrated in both embodiments of the invention is capable of both forward and reverse displacements by movement of the swash plate in one direction or the other from its neutral position.

The pump illustrated in the two embodiments is of the kind in which the cylinder block rotates. It is within the scope of the present invention to provide a swash plate pump of the kind in which the cylinder is non-rotary and the swash plate is rotated with the drive shaft.

Within the broad scope of the present invention the swash plate pump need not be arranged as a variable delivery pump, i.e., the angular setting of the swash plate may be fixed. Control of the transmission pump may then be effected by an unloading valve capable when desired of by-passing the pump delivery to a low pressure zone. In such a case closing of the by-pass valve will cause the pump to deliver liquid at pressure to the motor.

Whilst the twoembodiments of the invention disclose tilting head motors in which the tilting head is supported by arcuate lands to facilitate tilting movement of the head, it is equally within the scope of the present invention to use the equally well known form of tilting head motor in which the tilting head includes a yoke carried in trunnions for tilting movement about the tilt axis. In such a case the hydraulic connections to the motor would preferably pass through the trunnions and through passages in the yoke.

What is claimed is:

1. A hydrostatic power transmission comprising in combination,

(A) a swash plate pump comprising,

(i) a pump cylinder block having cylinders there- (ii) a pump drive shaft,

(iii) a swash plate,

(iv) pistons in the cylinders reciprocated by the swash plate by rotation of the pump drive shaft,

(B) a tilting head motor comprising,

(i) a motor drive shaft,

(ii) a tilting head tiltable about an axis transverse to the shaft axis,

(iii) a rotary motor cylinder block in the head having cylinders therein,

(iv) pistons in the cylinders reciprocated by shaft rotation with a stroke dependent on the tilt angle of the tilting head,

(C) hydraulic connections between the swash plate pump and the tilting head motor such that liquid at pressure delivered by the pump and fed to the motor will cause rotation of the motor drive shaft.

2. A hydrostatic power transmission as claimed in :laim 1 including arcuate lands on which the tilting head s tiltable by sliding movement along the lands.

3. A hydrostatic power transmission as claimed in laim 2 wherein the pump cylinder block and the motor :ylinder block are arranged in side by side relation and ncluding valve means for the pump cylinder block and 'alve means for the motor cylinder block arranged at imilar ends of the pump and motor cylinder blocks.

4. A hydrostatic power transmission as claimed in :laim 1 including a constant velocity universal joint nterconnecting the motor cylinder block and the motor lrive shaft.

5. A hydrostatic power transmission as claimed in :laim 3 including a plurality of connecting rods articuatingly secured one to each piston, a drive flange fast vith the motor drive shaft into which the connecting ods are pivotally connected and limited articulation means for each piston to limit the articulation of each aiston relative to its connecting rod thereby providing a 'otary drive from the drive flange to the cylinder block.

6. A hydrostatic power transmission as claimed in :laim' 5 including slippers mounted on the connecting rods ind rotatably driven by the drive flange and a wear plate tdjacent to the drive flange against which the slippers [1'6 adapted to react their axial load relative to the lrive flange axis.

7. A hydrostatic power transmission as claimed in claim L wherein the pump cylinder block is rotatably driven )y the pump drive shaft.

8. A hydrostatic power transmission as claimed in claim 1 including a shaft extending completely through the pump cylinder block and the pump swash plate.

9. A hydrostatic power transmission as claimed in claim 8 wherein the shaft extending through the pump cylinder block and swash plate also extends through the pump drive shaft.

10. A hydrostatic power transmission as claimed in claim 1 including a casing containing the pump and the motor and forming a reservoir for working liquid for the pump and the motor.

11 A hydrostatic power transmission as claimed in claim 3 wherein the motor tilting head is arranged such that during tilt movement thereof to reduce motor displacement it will move closer to the pump cylinder block.

12. A hydrostatic power transmission as claimed in claim 9 including a mechanical input connection for the transmission and gearing connecting the input connection both to the pump drive shaft and to the shaft extending through the pump drive shaft such that the two shafts rotate at different speeds.

13. A hydrostatic power transmission as claimed in claim 12 in which the gearing is arranged to rotate the pump drive shaft at a higher speed than the shaft passing through it. I

14. A hydrostatic power transmission as claimed in claim 2 including a connecting block which carries the arcuate lands for the motor and the valve means for the pump cylinder block.

15. A hydrostatic power transmission as claimed in claim 14 wherein the pump cylinder block is connected for rotation by the pump drive shaft and the valve means comprises a valve plate mounted on the connecting block.

16. A hydrostatic power transmission as claimed in claim 14 wherein the connecting block includes passages extending between the pump valve means and ports in the arcuate lands. to form the hydraulic connections between the swash plate pump and the tilting head motor.

References Cited UNITED STATES PATENTS 3,372,545 3/1968 Hyde. 3,419,096 12/1968 Zagotta. EDGAR W. GEOGHEGAN, Primary Examiner US. Cl. X.R. 1'8066 

